Currently, a wavelength division multiplexing technology, especially a dense wavelength division multiplexing technology has become one of main technologies used to implement high-speed and large-capacity data transmission in the optical communications field. In order to implement wavelength division multiplexing, a multiplexer is required to combine multiple light beams of different wavelengths into one light beam.
FIG. 1 is a multiplexer provided in the conventional art. As shown in FIG. 1, an existing multiplexer includes a rhombic prism. One side of the rhombic prism is coated with an anti-reflection film and a high reflection film, and four thin-film filters are attached to another side of the rhombic prism. The anti-reflection film improves light transmission, and the high reflection film improves light reflection. Filter characteristics of the thin-film filter make a light beam of a specified wavelength be transmitted and a light beam of a non-specified wavelength be reflected. The four thin-film filters have different filter characteristics from each other.
An incident light beam λ1, an incident light beam λ2, an incident light beam λ3, and an incident light beam λ4 are four light beams of specified wavelengths to be combined. The incident light beam λ1 enters the rhombic prism from a thin-film filter T1, and is reflected to another thin-film filter T2 at the high reflection film, and then reflected to the high reflection film by the another thin-film filter T2; the incident light beam λ2 enters the rhombic prism from the thin-film filter T2; and the incident light beam λ1 and λ2 are combined into one light beam at the thin-film filter T2.
The combined incident light beam λ1 and λ2 enter the high reflection film, and is reflected to another thin-film filter T3 at the high reflection film, and then is reflected to the high reflection film by the another thin-film filter T3; the incident light beam λ3 enters the rhombic prism from the thin-film filter T3; and the incident light beam λ1, λ2, and λ3 are combined into one light beam at the thin-film filter T3.
The combined incident light beam λ1, λ2, and λ3 enter the high reflection film, and is reflected to another thin-film filter T3 at the high reflection film, and then is reflected to the high reflection film by the another thin-film filter T3; the incident light beam λ4 enters the rhombic prism from a thin-film filter T4; the incident light beam λ1, λ2, λ3, and λ4 are combined into one light beam at the thin-film filter T4, and the combined incident light beam λ1, λ2, λ3, and λ4 enters the anti-reflection film and emerges from the anti-reflection film.
In the foregoing conventional art, although the combining four light beams of different wavelengths into one light beam is implemented, the multiplexer has six optical reflection points, the incident light beam λ1 is reflected six times, the incident light beam λ2 is reflected four times, and the incident light beam λ3 is reflected two times, and thus the four light beams are reflected twelve times totally. The light is reflected for many times in the multiplexer. The light is reflected for many times in the multiplexer, so during a reflection process, the incident light beams λ1, λ2, λ3, and λ4 are combined into one beam in sequence, and the four incident light beams are overlapped inside the multiplexer in sequence, which makes that, during a process of implementing light beam combination, an incident position and an incident angle of each incident light beam, and precision of the multiplexer are highly required, and thereby causing difficulties in manufacturing.